The UN atomic agency's board approved on Thursday, with a crushing majority, a resolution criticizing Iran, AFP reported.
The resolution expresses "serious concern that Iran continues to defy" UN Security Council resolutions for it to suspend uranium enrichment, a process which can be used for peaceful purposes but also in a nuclear weapon.
It also highlights the International Atomic Energy Agency's complaint that activities at the Parchin base near Tehran, where it suspects nuclear weapons research took place, would “significantly hamper” inspectors should Iran let them visit.
The resolution was introduced at the meeting of the IAEA's 35-nation board of governors on Wednesday after days of haggling between Western nations and Russia and China, which are seen as more lenient on Tehran.
It was approved Thursday by 31 countries, with Cuba voting against and Egypt, Ecuador and Tunisia abstaining.
“I think this resolution sends a very clear signal to Iran that the diplomatic pressure is intensifying and Iran's isolation is growing," U.S. envoy to the IAEA Robert Wood was quoted by AFP as having told reporters after the vote.
"The time right now is for compliance over defiance and Iran needs to comply now with its obligations.... We hope that Iran will hear and understand the message and begin to cooperate with the agency," he added.
"We are determined, with those countries that are ready, to further increase sanctions against Iran, as long as it continues to refuse to comply with its international obligations," French foreign ministry spokesman Vincent Floreani said in a statement.
Iran's envoy Ali Asghar Soltanieh hit back at the resolution, saying it “is not the way to resolve the Iranian nuclear issue. It will only complicate the situation and jeopardize the cooperative environment.”
The IAEA resolution stopped short of referring Iran to the Security Council, but it was significant that Western nations were able to get Moscow and Beijing on board.
The resolution "reflects the desire of member states to underscore that diplomacy is paramount and it warns Israel in two separate paragraphs that the diplomatic process should be supported," Mark Hibbs from the Carnegie Endowment for International Peace told AFP.
The IAEA's latest report on August 30 said that Iran had doubled since May the capacity at the underground Fordo site by installing around 1,000 new centrifuges.
Last week it was reported that several European Union nations are exploring a new raft of sanctions against Iran as exasperation mounts over blocked talks on the country's contested nuclear program.